Effect of stratification on combustion characteristics and thermoacoustic instability of hydrogen-enriched propane-air flames in a DACRS combustor

Hydrogen-enriched stratified swirl combustion is a promising approach for achieving stable and low-emission operation in advanced gas turbine systems. The combined effects of stratification and hydrogen enrichment on swirl-stabilized combustion remain insufficiently characterized in dual-annular counter-rotating swirl (DACRS) combustors. This study presents an experimental investigation of the effect of stratification ratio (SR) on hydrogen-enriched propane-air flames in a DACRS combustor. Experiments were performed over stratification ratios (SR = 1–3) and global equivalence ratios ( ϕ _ɡ = 0.5–1) at a fixed hydrogen fraction (HF = 40% by volume). Lean blowout limits (LBO), flame shape topology, temperature fields, emissions, and thermoacoustic response were systematically characterized. Dynamic pressure measurements were synchronized with CH*/OH* chemiluminescence diagnostics to characterize pressure-heat-release coupling. Hydrogen enrichment and stratification significantly extended the lean stability limits. In premixed operation (SR = 1), the LBO limit decreased from ϕ _ɡ = 0.52 to 0.41 (21% extension), and further to 0.34 at SR = 3, corresponding to a 34.6% extension. Increasing SR strengthened inner-root anchoring and promoted the formation of compact double-branch flame structures. NOx increased with SR and ϕ _ɡ due to higher local temperatures in the enriched inner annulus. Strong limit-cycle oscillations were observed at SR = 1, with dominant frequencies between 491 and 560 Hz. Increasing SR reduced oscillation amplitudes and suppressed limit cycles for SR ≥ 2. High stratification attenuated pressure-heat-release coupling and improved thermoacoustic stability. These results provide experimental benchmarks for the development of stable, low-emission, and fuel-flexible gas turbine combustion systems.